1. Field of the Invention
The present invention relates to a protective agent feeding member, a protective layer forming apparatus using the protective agent feeding member, and an image forming apparatus containing the protective layer forming apparatus.
2. Description of the Related Art
In conventional electrophotographic image formation, a visible image is formed by forming a latent image of electrostatic charges on an image bearing member of a photoconductive substance (referred to also as “latent electrostatic image bearing member,” “electrophotographic photoconductor,” or “photoconductor”), and adhering charged toner particles to the latent electrostatic image. The visible image formed by the toner is finally transferred onto a recording medium such as paper and is fixed on the recording medium, for example, by heat, pressure, a solvent, or gas to form an output image.
Electrophotographic image forming methods are roughly classified according to toner particle charging methods for visualization into the so-called two-component development method using tribocharging by stirring or mixing of toner particles and carrier particles and the so-called one-component development method in which charges are applied to toner particles without the use of carrier particles. The one-component development method is more advantageous in space saving and cost reduction than the two-component development method. Accordingly, the one-component development method is mainly used in small printers, facsimile machines and the like.
In these electrophotographic image forming apparatuses, a method is adopted that contains uniformly performing charging while rotating an image bearing member generally having a drum or belt shape regardless of a development method, forming a latent image pattern by laser beams or the like on the image bearing member, visualizing the latent image pattern by a developing unit, and further transferring the visualized image onto a recording medium.
A toner component that remains untransferred stays on the image bearing member after the transfer of the visible image on the recording medium. When the residual toner component is conveyed as it is without being processed to thereby perform a charging step, even charging of the image bearing member is sometimes hindered. Accordingly, a method is generally adopted in which, after the transferring step, the toner component and the like that stay on the image bearing member are removed by a cleaning step to satisfactorily clean the surface of the image bearing member, followed by charging.
In recent years, due to a reduction in size and a reduction in cost of electrophotographic image forming apparatuses, a contact charging method and a proximity charging method are mainly used in the charging step in the image formation. It is, however, difficult to evenly electrify the surface of the image bearing member due to, for example, a slight unevenness of the contact between the charging unit and the surface of the image bearing member and a variation in gap between the charging unit and the surface of the image bearing member. For this reason, an AC superimposed charging method has been used, and in this method an alternating current AC component is superimposed on a direct current DC component.
The proximity charging method by the AC superimposed charging can realize a reduction in size of a device and an improvement in image quality and, at the same time, renders the charging unit and the image bearing member non-contact while maintaining even charging. Thus, deterioration in the charging unit can be suppressed.
When the image bearing member is an organic photoconductor (OPC), the energy of the AC superimposed charging, however, cuts molecular chains of the resin forming the surface of the image bearing member, resulting in lowered mechanical strength that leads to remarkably progressed abrasion of the image bearing member. Further, since the AC superimposed charging activates the surface of the image bearing member, a problem occurs that the adhesion between the surface of the image bearing member and the toner increases and, thus, the capability of the image bearing member to be cleaned is lowered.
On the other hand, a recent tendency towards color output images has led to the development of toners that have smaller particle diameters and are circular, for improved image quality and image quality stabilization purposes. This tendency poses an increasing problem of cleaning in the electrophotographic image formation method. In order to remove the residual toner by cleaning, it is necessary to apply a higher rubbing force of the cleaning unit against the image bearing member than the force applied in the conventional technique. Accordingly, there is a problem of remarkable abrasion of the image bearing member, the cleaning unit and the like.
In each step for the electrophotographic image formation, electrical stress and physical stress exist. The image bearing member that has undergone these stresses causes a change in the surface state with the elapse of time.
Coating a protective agent on the image bearing member is known to be effective for solving the above problems. Examples of proposals for coating include one in which a block-shaped protective agent formed mainly of zinc stearate, a so-called protective agent block, is coated on an image bearing member (see Japanese Patent Application Publication (JP-B) No. 51-22380) and one in which a protective agent block prepared by adding boron nitride to a protective agent block formed mainly of zinc stearate is coated on an image bearing member (see Japanese Patent Application Laid-Open (JP-A) No. 2006-350240).
Coating the protective agent block onto the image bearing member lowers a coefficient of friction on an image bearing member to reduce a deterioration in a cleaning blade or an image bearing member and to improve the separation of an adhered material such as an untransferred toner adhered on the image bearing member. As a result, a failure of cleaning and occurrence of filming with the elapse of time can be suppressed.
Further, regarding a technique for coating a protective agent block onto the image bearing member, a proposal has been made on a protective layer forming apparatus containing: a protective agent block; a protective agent feeding member formed of a brush-shaped rotary member that is brought into contact with the protective agent block and coats the protective agent, which has been adhered on the surface, onto an image bearing member; and a protective agent pressing member that presses the protective agent block to allow the protective agent block to be brought into contact with the protective agent feeding member (see JP-A No. 2007-65100 and JP-A No. 2007-293240).
In these proposed techniques, however, a large amount of a protective agent powder produced from the protective agent block by rubbing with the brash-shaped rotary member, and is blown into the air by the rotation of the brush-shaped rotary member. Therefore, this poses a problem that a large amount of the protective agent is wasted. Further, the above techniques are disadvantageous in that bristle inclination or deterioration of brush fibers occurs with the elapse of time, the consumption of the protective agent is not stable, and the protective agent cannot be fed at a given amount over a long period of time.
Therefore, a technique has been proposed in which a roller-shaped protective agent feeding member containing a foam layer is used as a protective agent feeding member in a protective layer forming apparatus (Japanese Patent Application Laid-Open (JP-A) No. 2009-150986). According to this proposal, flying of the protective agent powder by rubbing hardly occurs.
In this proposed technique, however, the roller-shaped protective agent feeding member containing the foam layer is so soft that the force that shaves the protective agent block is small. Therefore, the protective agent cannot be satisfactorily fed to the image bearing member, and it is difficult to satisfactorily suppress filming of the image bearing member. Further, an attempt to press the protective agent block at a high pressure to increase the amount of the protective agent block shaved by the protective agent feeding member causes the application of a large load to the protective agent block and makes it impossible to evenly shave the protective agent block in a longitudinal direction. Consequently, the amount of the protective agent fed in a longitudinal direction of the protective agent block is disadvantageously varied. As a result, at a site in an image bearing member where the amount of the protective agent fed is small, the protective effect by the protective agent cannot be attained and filming occurs.
Accordingly, at the present time, there is a demand for the provision of a roller-shaped protective agent feeding member containing a foam layer that is substantially free from flying of a protective agent powder by rubbing, eliminates the need to increase the consumption of the protective agent, and can prevent filming, a protective layer forming apparatus using the protective agent feeding member, and an image forming apparatus containing the protective layer forming apparatus.